On this audio file, at 1:25, shouldn't it be
Source: The ILI English Series, Intermediate 2, Page 87
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You can use either their or your.
Their refers directly to the headlights' position.
Your position means the position that your headlights are in. It is your position because they are your car's headlights.
It is like someone talking about your mobile phone and saying your memory is full (which equals the memory on your mobile phone is full). You could also say its memory is full.